1. Field of the Invention
This invention relates to a push-push oscillator, and particularly to a push-push oscillator for high-frequency radio, communication, and measuring apparatus.
2. Description of the Prior Art
A prior art TEM mode resonator is frequently used for a high-frequency miniaturized resonator comprising an open-end half-wave resonator and U-shaped resonator. This is described in many publications. FIG. 13 shows an example of open end half-wave resonator comprising a resonating transmission line 101. FIG. 14 shows a resonator 102 formed into U-shape by bending the resonating transmission line.
A prior art push-push oscillator using the above-mentioned resonator as a high-frequency oscillator is frequently used, which is described in "Push-Push VCO Design with CAD Tools" (Zvi Nativ and Yair Shur, Microwave Journal February 1989).
FIG. 15 shows a schematic circuit diagram of such prior art push-push oscillator. The push-push oscillator comprises a resonating portion 103, an oscillating portion 104 including two symmetric oscillators such as Colpitts oscillators, whose two outputs have a phase difference of 180.degree. with each other, and a combining circuit 105 including transmission lines having the same electrical length for cancelling fundamental components and odd-order harmonic components and doubling only even-order harmonic components.
However, there is a problem that the size of the resonator 103 cannot be reduced because an area used for the resonator 103 is large to obtain a desired resonance frequency. This is because in the prior art resonator 103, the length of the resonator 103 is a half-wave which is large. Moreover, there is also a problem that a noise characteristic is poor because the combining circuit 105 of the push-push oscillating circuit combines the in-phase components with each other, so that externally incoming noise (in-phase) is doubled.